A microbiome is a collection of microorganisms known as microbiota. The human microbiome refers to the 10 to 100 trillion microbial cells that reside in the body. The majority of those cells are located within the gut microbiome, which is best known for its impact on the digestive system, immune system, and central nervous system.

But how much do you know about your skin microbiome and the role it plays in maintaining healthy skin? In this article, we'll review the myriad bacteria that live on the human body's largest organ and share the best ways you can maintain a healthy skin microbiome.

What Is the Skin Microbiome?

The skin microbiome — also referred to as the skin flora — is the diverse community of microbiota that is present on your skin. Elizabeth A. Grice and Julia A. Segre of the National Institutes of Health in Bethesda, Maryland, studied the skin microbiome extensively to "gain insight into microbial involvement" in various skin diseases and disorders. For their 2011 article published in Nature Reviews Microbiology, Grice and Segre break down the habitat of the skin as follows:

• Squames: Known as keratinocytes, these flakes make up 90% of the skin's outer layer (epidermis).
• Sweat glands: These include eccrine glands (which regulate temperature) and apocrine glands (which give off odor/pheromones).
• Pilosebaceous unit: This is composed of sebaceous glands, the hair shaft, and hair follicles to provide an antibacterial shield.

Bacterial Community of the Skin Microbiome

Within this habitat is a variety of microbiota — bacteria, fungi, viruses, and arthropods (small insects like mites). Bacteria make up most of the skin microbiome. According to Nina N. Schommer and Richard L. Gallo of the University of California, the bacterial skin microbiome consists of:

• Actinobacteria (51.8%): Decompose sebum (oil) and typically found on the upper chest, back, nostrils, and scalp.
• Firmicutes (24.4%): Producers of lactic acid that control the growth of other microbiota and are usually located in moist areas of the body such as the armpits.
• Proteobacteria (16.5%): Disease-causing bacteria that may include salmonella, E.coli, and cholera.
• Bacteroidetes (6.3%): Usually found in the gut microbiome but when found on the skin they can create infections.

The bacteria that are responsible for common skin conditions include:

• Propionibacterium acnes: As the name suggests, this strain is responsible for the development of acne vulgaris.
• Cutibacterium acnes (propionibacterium acnes): A slow-growing commensal bacteria that can not only cause acne but other potentially life-threatening conditions.
• Corynebacterium: This bacteria causes erythrasma, an infection that creates itchy, scaly skin under the arms, near the groin, or other moist areas of the skin.
• Staphylococcus aureus (staphylococci): Colloquially known as "staph," the strain level of this bacteria can cause anything from abscesses and cellulitis to methicillin-resistant Staphylococcus aureus (MRSA), which is often picked up in hospitals or health care facilities.
• Streptococcus pyogenes (streptococci): Commonly found on the skin and in the throat, this bacterial species can lead to the development of scarlet fever, impetigo, and strep throat.

Bear in mind that not all bacteria are bad. Probiotics — good bacteria — that are present on the skin play an important role in protecting the skin from inflammation and infection. Some of these beneficial skin bacteria are:

• Roseomonas mucosa: A 2017 article in JCI Insight reported a decrease in atopic dermatitis (also known as eczema) via topical application of R. mucosa.
• Lactobacillus plantarum: Per a 2012 study published in the Journal of Cosmetic Science, L. plantarum can be used to heal mild acne lesions.

A note about Staphylococcus epidermidis: Michael Otto, Ph. D., dubbed Staphylococcus epidermidis "the 'accidental' pathogen" in a Nature Reviews Microbiology from 2009. On the one hand, S. epidermidis is associated with skin infections that develop from implanted medical devices, such as a catheter.

However, a 2018 study featured in Science Advances discovered that strains of S. epidermidis that produce the molecule 6-N-hydroxyaminopurine (6-HAP) may offer protection from skin cancer.

Fungi, Viruses, and Arthropods Within the Skin Microbiome

In addition to good and bad bacteria, your skin flora is also composed of fungi, viruses, and arthropods. These can create a number of skin issues and infections if your skin microbiome is unbalanced.

Fungal Infections

Also known as mycosis, fungal infections can lead to redness, itching, and scaling. They occur in damp areas of the skin and are seldom life-threatening, although they can be contagious. Common fungal infections include:

• Ringworm (tinea corporis): A ring-shaped rash that is found on the torso.
• Athlete's foot (tinea pedis): An infection that causes itching, burning, and blisters on your feet.
• Jock itch (tinea cruris): Typically situated in the groin area but can also spread to the buttocks and abdomen, it's a flaky red rash that's common among males.
• Candidiasis: An overgrowth of the Candida yeast that causes dry, red skin around the mouth (thrush) or vaginal itching (yeast infection).
• Fungal acne (Malassezia (Pityrosporum) folliculitis): A result of an overgrowth of Malassezia yeast in cutaneous flora that yields papules and pustules on the chest, back, arms, and face.

Viral Infections

Viral skin infections are highly contagious and can be fatal if not treated promptly and properly. These include:

• Molluscum contagiosum: A chronic condition that is characterized by small pearl-sized bumps with dimpled centers that are sometimes itchy.
• Measles: A virus that produces a red rash all over the body along with a cough, fever, sore throat, and white spots inside the mouth.
• Warts: An infection caused by the human papillomavirus (HPV) that can potentially lead to certain types of cancers.

Arthropod-Borne Infections

An arthropod can be an insect, spider, or crustacean. Skin infections from arthropods are usually the result of a bite or general contact. Examples of arthropod-borne infections are:

• Rosacea: Demodex folliculorum mites that live on human skin can cause the inflammation and flushing that's associated with this skin condition.
• Blepharitis: Another skin condition brought forth by demodex folliculorum mites, this impacts the eyelids by making them crust over and itch.
• Lyme disease: Spread by ticks that carry borrelia bacterium, resulting in a rash and flu-like symptoms.

How to Maintain Healthy Skin Microbiome

As you can see, your skin microbiome is a complex composition of microorganisms that must be balanced accordingly. But what are the best ways to maintain harmony among human skin microbiota? The suggestions below will ensure that your body's largest organ is healthy and balanced.

1. Don't Use Harsh Cleansers

When it comes to cleansers, especially for your face, you want something that is effective at removing impurities and pathogenic bacteria and other flora without stripping your skin's barrier for protection, including probiotics that help fight infection.

Avoid formulas with a very high pH — the optimal pH for skin is around 5. The YORA Rebalance Face Cleanser has an average pH level of 6, which means it can gently wash away any dirt, oil, and impurities without damaging your skin barrier.

As for the rest of your body, especially your hands, antiseptic or antimicrobial soap is not necessary, per the United States Food and Drug Administration. Washing with regular soap and water is still regarded as the best way to keep yourself safe from germs without eliminating good bacteria.

2. Consider Following a Microbiome Diet

The microbiome diet is focused on recalibrating and maintaining a healthy gut microbiome. But as this 2018 article from Frontiers in Microbiology points out, a well-regulated gut microbiome can yield benefits throughout the rest of the body, including the human skin microbiome. In particular, a stable gut microbial ecology can play an important role in skin homeostasis (how the skin regenerates itself) and skin allostasis (the restoration of skin homeostasis following a disturbance).

A microbiome diet is rich in probiotics, which can be found in fermented foods like kimchi, kefir, miso, and yogurt. It also contains prebiotics, on which probiotics feed. Onions, bananas, leeks, and asparagus are just some of the foods that contain prebiotics.

The goal of a microbiome diet is to repair your gut microbiome, and by extension the rest of your body. It can be particularly restrictive as dairy, soy, eggs, yeast, and gluten are among some of the things that must be cut from your diet. As with any new nutrition plan, consult your doctor or healthcare professional first before proceeding.

3. Practice Stress Management

Stress can impact the state of your gut microbiome, per a 2017 article published in Neuropsychopharmacology. And what affects your gut flora can also affect your skin flora. High levels of stress can weaken your body's immune response, which can have a negative effect on the first line of defense, your skin. Practice meditation or yoga, or immerse yourself in a relaxing hobby to keep stress at bay.

The Ideal Skin Microbiome Encourages Microbial Diversity

Your skin microbiome is always in flux. It's colonized as soon as you're born and alters throughout your life depending on your environment and lifestyle choices.

It's important to remember that not all bacteria are bad. Harsh cleansers and bactericidal soaps may be promoted as effective ways to remove germs and impurities, but they also eliminate the probiotics that prevent pathogenic bacteria and other harmful microbiota from developing into infections and diseases. A relative abundance of good bacteria should remain on your skin surface as a barrier.

Microbiome research shows that the gut-skin axis is key in maintaining healthy, normal skin. Introducing more probiotic- and prebiotic-rich foods into your diet will ultimately benefit the microflora that resides on your skin.

This is yet another reason why a wholistic approach to skincare is important. Healthy skin does not begin and end with the products you use. A higher-level understanding of the habits you cultivate, and how they affect your overall well-being, will benefit your general skin health.